\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx,bm}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide,ninecolors}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
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  \draw(-1.5,0.3)--++(120:0.8)node[above]{电子束};
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  \node at (3.2,-0.64)[above]{$+$};
  \node at (-3.2,0.64)[above]{$-$};
\end{tikzpicture}
\end{document}